1. Field of the Invention
This invention relates to a method for making a flocculant composition.
2. Description of the Prior Art
The polyacrylamide-type flocculants have been known for at least about 20 years. They have been made by polymerizing acrylamide alone or with a comonomer, such as acrylic acid in the case that a flocculant of the anionic type is desired, or with, e.g., dimethylaminoethyl methacrylate (DMAEMA) or diethylaminoethylacrylate (DEAEA), in the case that flocculant of cationic nature is desired. Other comonomers, such as acrylonitrile, methacrylic acid, and the like, have also been used.
The prior practices have various shortcomings.
When solution polymerization is used, it is ordinarily not possible to obtain a liquid product which contains more than about 5 to 7 percent by weight of the active-ingredient polymer. Polymers of this kind, useful as flocculants, have high molecular weights, on the order of 1,000,000 or more, and they form in water very viscous solutions, even when they are present at low concentrations such as 2 or 3 percent. The chief drawback of water-based liquid products is that they are uneconomical to store and to ship, because they must contain such a great percentage of water if they are not to become too viscous. More over, dilute polymer solutions are subject to degradation.
Solid polyacrylamide-type flocculant products have been made. They are convenient to ship and to store, but they have the drawback that they often require the use of special equipment to dissolve them in water at the site of the intended use, and in many cases, such dissolution does not happen rapidly.
Still another approach is that of U.S. Pat. No. 3,637,491, in accordance with which the polymerization is conducted in a water-in-oil emulsion, and then, with a surfactant material being provided either in the polymer-containing composition or in the water to which it is later added, the water-in-oil emulsion is then added to a larger quantity of water and the emulsion is consequently inverted, to form an oil-in-water emulsion. With this approach, it is possible to obtain a composition which provides a substantial content of polyacrylamide-type active ingredient, such as 20 or 30%, but the method has a considerable drawback in that a large proportion of oil, which is not biodegradable and is thus subject to objection under the laws and regulations concerning pollution, is necessarily present in the emulsion-type products of the kind mentioned above.
Still another approach is that of British Pat. No. 1,397,933, in which there is first made a solid flocculant, which is then ground very fine in a ball mill or the like and then added to mineral oil. Although this approach yields a liquid which is pumpable and contains the flocculant material in finely divided form, so that it can readily be dissolved in water at the point of use, this approach is not convenient and is not inexpensive. The grinding step is especially costly, and the product contains mineral oil, which is not readily biodegradable.